Field of the Invention
The invention relates to a duct piece for a flue-gas duct of a gas turbine having a number of sound-absorber panels. The invention also relates to a flue-gas duct and a gas and steam turbine plant.
Gas turbines are used in many sectors for driving generators or machines. The energy content of a fuel is utilized in gas turbines to produce a rotary movement of a turbine shaft. A working medium or hot gas resulting during combustion of the fuel is expanded in the gas turbine for that purpose and is then fed as exhaust gas or flue gas to a flue-gas duct attached to the gas turbine.
In order to increase overall efficiency, a waste-heat steam generator may be disposed downstream of the gas turbine in the flue-gas duct. In the waste-heat steam generator the energy content of the fuel remaining in the flue gas as heat is utilized to evaporate a working medium carried in a water/steam cycle of a steam turbine. Such a combined plant for generating electrical energy is also referred to as a gas and steam-turbine plant (G & S plant).
The flue-gas duct of the gas turbine normally includes a plurality of components or duct pieces connected to one another. Depending on the structure and the location of the gas turbine, a diffuser, an exhaust-gas duct with or without a bypass stack, and further elements, such as, for example, a gas switch and a waste-heat boiler, are provided as components.
During operation of the gas turbine, each component of the flue-gas duct is normally heated by the exhaust gas or flue gas flowing through the components. Heat insulation of the components of the flue-gas duct is therefore normally provided. That may be external insulation, in which the insulating elements are disposed in the external region of the respective component. Alternatively, internal insulation, in which the insulating elements are disposed in the internal region of the respective component, may be provided.
When a gas-turbine plant, in particular a gas and steam-turbine plant, is being constructed, requirements for sound absorption have to be taken into account. For example, an overall sound power level according to ISO 3746 of the entire flue-gas duct of the gas turbine which must not exceed 90 dB(A) may be required. Furthermore, for example, an average sound pressure level which must not exceed 85 dB(A) at a distance of about one meter from components of the flue-gas duct and a sound pressure level which must not exceed 55 dB(A) at a distance of 120 m from the outer limits of the entire plant may be required. In order to fulfill such noise requirements, a number of sound-absorber panels are normally provided in the flue-gas duct of the gas turbine. In a gas and steam-turbine plant having a flue-gas duct which contains a bypass stack, a first set of sound-absorber panels is normally disposed downstream of the waste-heat boiler and a second set of sound-absorber panels is normally disposed in the bypass stack. Such a type of construction is normal, in particular in the case of a vertically disposed, externally insulated waste-heat boiler. German Published, Non-Prosecuted Patent Application 28 55 5219, for example, discloses a gas-turbine waste-heat boiler in which a number of sound absorbers are disposed.
In order to increase the efficiency of a gas and steam-turbine plant, it is possible, for example, to increase the combustion temperature in the gas turbine and thus also the temperature level in the entire flue-gas duct disposed downstream of the gas turbine. However, for technical reasons related to the material, it is necessary in that case to provide mainly internally insulated components for the flue-gas duct, in particular an internally insulated waste-heat boiler and an internally insulated diffuser. However, adequate sound absorption of those internally insulated components, in particular with regard to possible noise requirements, is expensive. To that end, jacketing or encasement of components is normally provided in addition to the sound-absorber panels provided anyway in the bypass stack and downstream of the waste-heat boiler. Such a type of construction and in particular the jacketing of the waste-heat boiler is only possible with high expenditure on material and insulation and is therefore uneconomical.